1. Field of the Invention
The present general inventive concept relates to a transfer apparatus, and more particularly, to a transfer apparatus having an improved structure to provide a super-precision transfer.
2. Description of the Related Art
Generally, a super-precision transfer apparatus is employed in a scanning apparatus for inspecting a semiconductor wafer, a liquid crystal display (LCD) panel or the like, and also employed in a semiconductor machining, a super-precision machining, etc.
Such a super-precision transfer apparatus includes a supporter, such as a frame mainly supporting a semiconductor wafer or the like, an actuator connected to the supporter and driving the supporter to move with respect to a reference plate; and a controller to precisely control the actuator.
There are various actuators typically used for a precise drive by employing an electric motor, a piezoelectric element, electromagnetic induction, etc. Particularly, a voice coil motor (VCM) using a linear motor is used as the precise actuator employing the electromagnetic induction.
The VCM is an actuator using a vibration mechanism of a speaker, following a principle that a permanent magnet is moved by a force in a direction orthogonal to a magnetic field and an electric current according to the Fleming's left hand law when the electric current flows in a voice coil located in the magnetic field due to the permanent magnet. Further, the VCM actuator is classified into a coil movable type and a magnet movable type. That is, in the coil movable type actuator, a voice coil is movable with respect to a stationary permanent magnet, while in the magnet movable type actuator, a permanent magnet is movable with respect to a stationary voice coil.
As a conventional precise transfer apparatus, a stage apparatus for a precise actuator using a magnet movable type VCM is disclosed in Korean Patent No.: 10-0407897 (Publication No.: 2003-20787).
As shown in FIGS. 1 and 2, such a stage apparatus 100, by way of example of a conventional precise transfer apparatus, includes an induction unit 10 which is stationarily seated in a through portion of a plate 20 and has a hollow shaft 12 and a coil 11 provided at opposite sides of the hollow shaft 12, which are exposed through the through portion, and a movable unit 30, which includes a pair of yokes 32 disposed symmetrically with the hollow shaft 12 and being straight movable or rotatable with respect to the hollow shaft 12 due to a magnetic field formed by the coil 11, and a pair of movable magnets 31 having different polarities and respectively attached to the yokes 32 using a magnetic force to interpose the coil 11 between the movable magnets 31.
Here, three induction units 10 are triangularly arranged in the plate 20 at an angle of 120° therebetween, and the movable magnet 31 is a permanent magnet. That is, three VCMs having the same motive power are equiangularly arranged on the plate 20.
Thus, in the conventional stage apparatus 100, the movable magnet 31 is driven to move with respect to the coil 11 by flowing the electric current in the coil 11 of the induction unit 10. Further, in the conventional stage apparatus 100, the three induction units 10 are arranged to form an equiangular triangle structure, and the movable unit 30 is straight movable (X and Y-directions) or rotatable (θ-direction) with respect to the plate 20 by selectively applying the electric current to at least one of three coils 11 provided in the induction coil 10.
However, in the conventional stage apparatus, because three induction units are arranged to form an equiangular triangle structure, there is generated a difference between the straight movements of the movable units in the X- and Y-directions. For example, referring to FIG. 1, the X-directional straight movement of the movable unit is based on an X-directional vector component of a resultant force of F1, F2 and F3, and the Y-directional straight movement of the movable unit is based on a Y-directional vector component of a resultant force of F2 and F3, so that the X-directional straight movement is greater than the Y-directional straight movement. Hence, the difference between such straight movements results in making it hard to decrease a positioning control error when a super-precision positioning control is required.
Further, in the conventional stage apparatus, when the movable units are driven to move in one of the X- and Y-directions, the movable unit is also driven to move in the other direction. For example, when the movable units are driven to move in the X-direction, some movable units are driven to move in the X-direction as well as the Y-direction, so that he movable units are driven to move in a direction different from the X-direction, thereby resulting in making it difficult to decrease the positioning control error when the super-precision positioning control is required.